CVE-2021-28931: Arbitrary file upload vulnerability in Fork CMS 5.9.2 allows attackers to create or replace arbitrary files in

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HIGH 8.8DOWNGRADE

CVE-2021-28931 is a high-severity flaw (CVSS 8.8) affecting fork cms. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Arbitrary file upload vulnerability in Fork CMS 5.9.2 allows attackers to create or replace arbitrary files in the /themes directory via a crafted zip file uploaded to the Themes panel.

Why this priority

High severity

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	8.8 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	1.2% (top 32%)
CISA exploited list	No
Weakness	CWE-434
Published	2021-07-07
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: fork-cms

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-07-07 15:15 UTCPublished CVE record published
2026-06-17 03:47 UTCUpdated Record last modified

fork-cms fork cms DOWNGRADE

Affected: 5.9.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 5.9.2

1. Check installed version

apt-cache policy fork-cms || rpm -q fork-cms || fork-cms --version

2. No fixed release: DOWNGRADE to a release before 5.9.2 (Debian / Ubuntu)

apt-cache madison fork-cms sudo apt install fork-cms=<VERSION_BEFORE_5.9.2> sudo apt-mark hold fork-cms

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list fork-cms sudo dnf downgrade fork-cms-<VERSION_BEFORE_5.9.2> sudo dnf versionlock add fork-cms

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-28931?

fork cms: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-28931 being exploited?

CVE-2021-28931 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-28931 affect?

CVE-2021-28931 affects fork cms. Severity is high (CVSS 8.8). Arbitrary file upload vulnerability in Fork CMS 5.9.2 allows attackers to create or replace arbitrary files in the /themes directory via a crafted zip file uploaded to the Themes panel.

How urgent is CVE-2021-28931?

Priority 48/100. High severity

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References

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